Mastering CIE 9702 Paper 5 requires moving beyond simple plotting to precise uncertainty analysis. While Question 1 tests your experimental design, Question 2 demands mathematical rigor. You must draw a Worst Acceptable Line (WAL)—the steepest or shallowest gradient passing through all error bars—to quantify your gradient uncertainty. To simplify this, use our Line of Best Fit Graph Maker to instantly verify your manual WAL and intercept calculations against exam standards.